There is currently an ever-increasing demand for light olefins in the petrochemical industry (Marcilly C., Studies in Surface Science and Catalysis 135, 37 (2001); Hydrocarbon Processing, Vol. 80, No. 6, p. 23 (2001)). Together with steam cracking, Fluid Catalytic Cracking (FCC) or its variant, Deep Catalytic Cracking (DCC), are the processes most used in the production of C3–C5 olefins. In particular, catalytic cracking produces large amounts of propylene, one of the olefins in greatest demand. Furthermore, FCC provides approximately 30% of the gasoline stream in a refinery, and at the present time when there is surplus global production of gasoline, particularly in Europe, the FCC unit's selectivity for propylene can be increased, optimizing the economic yield of the unit.
The amount of propylene produced by FCC may be increased by modifying the working conditions of the unit, for example by increasing the temperature of the reactor. However, this solution entails a considerable increase in gases, in particular in unwanted dry gas. Better results are obtained using novel catalyst compositions that involve the use of zeolite mixtures. The use of zeolite ZSM-5 as an additive in FCC catalysts also results in an increase in C3 and C4 olefins (see, for example, U.S. Pat. Nos. 3,758,403, 3,769,202; 3,894,931; 3,894,933; 3,894,934; 3,926,782; 4,309,280; 4,309,279; 4,375,458; and Buchanan, J. S. and Adewuyi, Y. G., Applied Catalysis A: General, 134, 247 (1996); Madon, R. J., Journal of Catalysis 129 (1), 275 (1991)). However, it is known (Studies in Surface Science and Catalysis, Vol. 76, 499 (1993)) that the introduction of zeolite ZSM-5 has little or no effect on the total conversion.
Both from the point of view of increasing the barrel octane number of the gasoline and of increasing the yield of C3–C4 olefins, particularly of propylene, it would be advantageous to find other zeolites that also make it possible to convert feed. Many medium- and large-pore zeolites have been studied for this purpose. Mention can be made of the use of zeolite MCM-22, Omega, L, mordenite and BEA (see, for example: J. Catal. 165, 102 (1997); Stud. Surf. Sci. and Catal. 46, 115 (1989); U.S. Pat. No. 5,314,612; EP-489 324; U.S. Pat. Nos. 4,740,292; 4,137,152; EP-350 331; FR-2 661 621).
Spanish patent application P200101145 discloses a novel zeolite, called ITQ-21, whose structure is defined by a characteristic X-ray diffractogram, as an active zeolite component for cracking organic compounds, more specifically petroleum-derived hydrocarbon fractions or synthetic fractions. The relative intensities, widths, and positions of the diffraction peaks can change depending on the chemical composition of the material, and on the degree of hydration and the size of the zeolite crystal.
However, the potential of zeolite ITQ-21 as a catalyst in processes for cracking and converting organic compounds has not been developed to date, and it forms the subject of the present invention.
It will be shown that the pore topology of this zeolite confers on it activity for cracking catalytic cracking unit feeds, and for obtaining, alone and/or in combination with other zeolites, a good octane number of the gasoline produced and a good yield of olefins, especially of propylene.